Nephelometer



Dec. 6, 1960 E. J. MARAK ETAL NEPHELOMETER 6 Sheets-Sheet 1 Filed June 4, 1956 ...gli

INVENTORS E.. J. MARAK BY H.W. STATEN QR.

A T Tom/EK;

Dec. 6, 1960 Filed June 4, 1956 6 Sheets-Sheet 2 INVENToRs E. J. MARAK H.w. STATENPJR.

E. J. MARAK Erm. 2,962,926

NEPHELOMETER De 6, 1950 E. J. MARAK ETAL 2,962,925

NEPHELOMETER Filed June 4. 1956 6 Sheets-Sheet 4 HMMQW Dec.6,196o EJ, MARAK Em 2,962,926

NEPHELOMETER Filed June 4. 1956 6 Sheets-Sheet 6 INVENTORS E. J. MARAK 999999299 F/G- /2- HW* (www ATTORNEYS H.W.STATEN,JR.

United rates Patent O NEPHELOIVIETER Eldon J. Marak, Dewey, and Hi W. Staten, Jr., Bartlesville, Okla., assignors to Phillips Petroleum Company, a corporation of Delaware Filed June 4, 1956, Ser. No. 589,242

Claims. (Cl. 88-14) This invention relates to the detection of solids suspended in iluids by means of light scattering measurements.

In various types of chemical processes it is necessary to separate solids from iluids. One particular need for such a separation occurs in the polymerization of olens by the use of granular catalysts. 'In this process it is important to separate the catalyst from the polymer in order to obtain a high purity product. The separation can be accomplished by means of conventional filters or centrifuges. In such an operation it is desirable to measure continuously the solid content of the iilter eiuent to be sure that the filtering means is making the desired separation.

In accordance with one aspect of the present invention, novel apparatus is provided to detect the presence of suspended solids in fluids. A beam of radiation is directed through a sample of the material to be analyzed. A portion of the beam is scattered by suspended particles in the fluid. A beam of this scattered radiation is compared with the transmitted beam to determine the concentration of the suspended particles. The comparison is accomplished by directing the two beams alternately on a radiation detector. The ratio of the scattered radiation to the transmitted radiation is a function of the solid particle concentration. The operation of the detector is regulated by the signal produced when the transmitted beam is received so that the signal of the scattered beam is independent of fluctuations in the light source.

A uid-solids separation system can be controlled by an output signal from the analyzer of this invention. In one embodiment of this control system, the iilter etiluent is diverted to a disposal line Whenever the solids concentrate exceeds a predetermined value. At the same time an alarm can be actuated to notify the operator.

Other control systems responsive to the analyzer output signal involve transferring the material to be separated from a rst lter to a second filter whenever it becomes necessary to regenerate or replace the iirst filter. In still another embodiment, a centrifuge is controlled by the analyzer output signal to maintain the desired separation.

Accordingly, it is an object of this invention to provide apparatus for detecting solids in lluid by means of light scattering measurements.

Another object is to provide improved apparatus for comparing radiation beams.

Other objects, advantages and Yfeatures of the invention should become apparent from the following detailed description, taken in conjunction with the accompanying drawing in which:

Figure l is a schematic ow diagram of an oleiin polymerization process having a irst embodiment of a control system incorporated therein;

Figure 2 is a perspective view of the solids detector of this invention;

Figure 3 is a detailed view of the optical system of the solids detector;

Figure 4 is a view taken -along line 4-4 in Figure 3;

Figure 5 is a view of the chopper which is rotated in the transmitted and scattered beams of radiation of the detector of Figure 3;

`Figure 6 is a schematic representation of the air purge and water cooling system of the detector;

Figure 7 is a schematic circuit diagram of the electrical components of the radiation comparing means;

Figures 8, 9, 10 and 1l are schematic representations of additional embodiments of the fluidsolids separation control system; and

Figure l2 is a modified form of comparing circuit.

Referring now to the drawing in detail and to Figure 1 in particular, there is shown a reactor lll which is provided with an agitator or stirrer 11 that is rotated by a motor 12. A ,feed conduit 13 communicates with reactor 10 to supply oleiins to be polymerized. A granular catalyst is introduced into reactor 10 through a conduit 14. A suitable solvent is introduced into the reactor through a conduit 15. `In some operations, the catalyst can be dissolved in the solvent and supplied through the same conduit. Reactor l0 is equipped with a jacket 16 through which a cooling uid is circulated by means of an inlet conduit 17 and an outlet conduit 18.

The eflluent product polymer is withdrawn from reactor ltl through a conduit 2t) which has a heater 21 therein. The purpose of heater 21 is to maintain the eiiiuent at a suficiently high temperature so that the polymer remains dissolved in the solvent Conduit 20 communicates with a flash chamber 22.. The polymer is removed from chamber 22 through a conduit 23. 'I'he vapor stream comprising the unreacted olen is removed from the top of chamber 22 thro-ugh a conduit 24 which has a condenser 25 therein. Conduit 24 communicates with a separator 26. The unreacted olen vapors are removed from the top of separator 26 through a conduit 27. Any condensed material is returned to chamber 22 through a conduit 30 which has a heater 31 therein.

A cond-uit 32 communicates with conduit 23 to supply additional solvent to the reaction product to ensure that the polymer remains in solution. A heater 33 is incorporated in conduit 23. The resulting mixture of product and solvent is directed to the inlet of a fluid-solids separator 35, which can be a lter or centrifuge, for example. The solids-free effluent from separator 3S is directed by a conduit 36 to the inlet of the solids detector 37 of this invention. From detector 37 the stream passes to the inlet of a two-way valve 3S. The inlet of valve 33 normally is in communication with an outlet conduit 39 which delivers the product to a storage tank, not shown. A second conduit 40 communicates with valve 38 so as to remove the product to a disposal tank whenever valve 38 is actuated by a signal from detector 37. Whenever the measured solids content exceeds a predetermined value, valve 38 is operated in this manner. An alarm 41 is also energized to indicate that the product is no longer of the desired purity.

While the contro-l system of this invention is applicable generally to any fluid-solids separation process, it is particularly applicable to the described polymerization process which involves the polymerization of l-olens containing no more than 8 carbon atoms per molecule and having no branching nearer the double bond than the 4fpositio-n. This polymerization can be performed by the use of a catalyst comprising chromium oxide supported on a base of silica, alumina or silica-alumina. As a specific example of this reaction, ethylene is supplied to reactor 10 at the rate of approximately 14.6 cubic feet per hour. One gallon of isooctane is supplied to the reactor in the same time. The catalyst is supplied at such a rate as to maintain from 0.1 to 0.5 weight percent catalyst in the eluent removed through conduit 20. Reactor is maintained at a temperature of approximately 285 F. andata pressure of approximately 500 pounds per square inch gage. The1reactor-eluent normally contains approximately 0.3 weight percent catalyst, 6.5 Weight percent polyethylene, 6.5 percent ethylene, 0.7 weight percent light gaseous impurities and.

86.0 weight percent solvent. The eflluent-is heated-to approximately 325 F. by heater: 21. A pressure of 100 pounds per square inch gage is maintained in chamber22,v and a pressure of 90 pounds per square inch gage is maintained ,in separator 26; The euent from condenser 25 enters separator 26- at a temperaturewof 100 Under these conditions, the bottoms product from chamber 22 contains 0.3 weight percent catalyst, 6.9 weight percent polymer, 1.1 weight percent ethylene, 0.1 weight per light gaseous impurities and 91.6 weight percent.l solvent. Gas is removed from separator 26 through conduit 27 at a rate of approximately 6.7 cubic feet per unit time. This gas has a composition of c 81 weight percent ethylene, l() Weight percent solvent and 9xweight percent light gaseous impurities.

It is to be understood,V however, thatthe polymerization process .is not limited to the specific example herein described. In some applications, diolens and conjugated diolens of no more than 8 carbon atoms per molecule can be polymerized. Other polymerization catalysts can be employed in some operations; and other bases, such as thoria and zirconia, can be employed. Suitable solvents include aliphatic and alicyclic hydrocarbonshaving 3 to 12 carbon atoms per molecule, and more.`

particularly such hydrocarbons having 5' to l2 carbon atoms per molecule. propane, normal butane, cyclohexane and methylcyclohexane. Furthermore, the reaction temperatures, pressures and feed rates can be varied. The l-oleins described herein can be polymerized at temperatures in the range of 150 to 450 F. and at pressures varying up to 700 pounds per square inch gage, or even higher in some instances. Temperatures in the rangeof 275 to 375 F. are preferred for ethylene, and temperatures in the range of 150 to 250 F. are preferred forpropylene. Mixtures of l-oleiins can also be polymerized. Detector 37 is illustrated in detail in Figures 2, 3, 4, and 5.' The optical and electrical components of 'the analyzer are mounted on a base plate 50 which is contained within an explosion-proof cylinder 51. Cylinder 51 is bolted 'to` a front panel 52 which is maintained in an upright position by a frame 53. A rod 54 is attached to cylinder 51 and rests on support bars 55. Asample of the stream to be analyzed enters cylinder 51 through a conduit 58 which extends through panel 52. Conduit-58 communicates with a passage 56-V formed in ametal block 57. The outlet of passage '56 communicates with conduit 58 which extends throughY panel52 to remove the sample stream from passage,l 56.g It is important that the sample stream be maintained at an elevated temperature in order to retain the polymer in solution. mounted in block 57 for this purpose. elements are regulated by a thermostat 61 which maintains the desired temperature. Bloch 57 preferably is surrounded by a mass of heat insulating material 62.

Block 57 is provided with a second passage 64 which` communicates with passage 56 at right angles thereto. A beam of radiation is `directed through passage 64 and throngthe sample fluid circulated through passage 56.

This'radiation beam is produced by a vlight source 65A which is mounted in a housing 66. Radiation from source 6Sis collimated'by a lens67 andpassed-th'rough an'aperture 68 so:thatl a narrow beam is directed through passage `6&1. The radiation- Ytransmitted through passage 64'-and thefuid vsamplelis reflectedy by a'prism 70' to Examples of such solvents include A plurality of heating'elernentsV 60 -are' These heatingimpinge upon a radiation detector 72, such as a photo multiplier tube. Prism 70 is mounted in a housing 71 and detector 72 is mounted in a housing 73. One or more attenuators 75 are positioned in the beam to reduce the intensity. A portion of the radiation beam directed through passage 56 is scatteredby the solid particles entrained in the sample uid and emerges from block 57 through a passage 77'. A window 78 prevents leakage of iluid from passage 77. This scattered radiation beam lis focused bylenses 8.0 and 81 through an aperture 82. The beam transmitted through aperture 82 is focused by lens 83 on detector 72.

A chopper `disc 85 is rotated in thel two radiation beams at a predetermined speed'by means of a motor 86. This disc, which is illustrated in detail in Figure 5, is provided with an annular slot 87 which extends nearly 180 so that each radiation beam is alternately blocked by and transmitted through the disc. Detector 72 thus receives radiation fromthe two beams alternately. A mechanical switch 90 is also actuated by a motor 86fso that the output signal from detector 721 is connected to one of the two Icircuits depending upon whichvbeam` The operation of this switch Switch 90 Aand the elecis received by the detector. is describd in detail hereinafter.

t-rical components associated therewith are mounted in a housing 91.

In order to maintain the operation ofthe loptical and electrical components of the analyzer uniform,v it .is nec-V essary that these components not be overheated. This' is accomplished by circulating a cooling fiuid, such-as water, through cylinder S1. The cooling Water enters cylinder 51 through panel 52 and is directed -by a conduit 93 to housing 73. The Water circulates through a pas-- sage in housing 73 and is directed therefrom through aconduit 94 to housing 66. The water circulates through'- a'conduit in housing 66 and is then directed through a conduit 95 to housing 91. The water circulates through' a conduit in housing 91 and is then directed through-ar` conduit 96 to housing 71. The water circulates through? a conduit in housing 71 and is vented through a conduitl 97 which passes out of cylinder 51 through pane1`52;

This circulating Water prevents the analyzer from beingelevated in temperature from the hot duid in block-57.V It is also desired to prevent the accumulationof hydro-l carbon vapors in cylinder 51 from possible leaks' inctheA sample system. This is accomplished by circulating'air' through cylinder 51 to purge any hydrocarbon vapors" from the cylinder. The apparatus illustrated inA Figures 2 and 6 is provided to supply filtered, moisture-free airj Air is supplied to the inlet of 'an'up4 for this purpose. right tube'100 through a conduit 101 which has apres;

sure regulator 102 and a pressure gage 103 therein'f Tube has a coil 105 positioned in the upper portion inlet conduit 93 in cylinder 51.

pressure gage 112 therein. Any condensible'vapors'in the air are condensed by contact with coil 1051and settle" to the bottom of tube 100 to form a column lof liquid.3

This liquid column is transmitted vby a passage 114'to the lower side of a diaphragm 115. Diaphragmfllllnor mally is urged by a spring 116 to a positionwhich blocks an outlet passage 117. It should be evident that as the' column of liquid increases in height the pressure exerted.

on the underside of diaphragm is increased soithat passage 117 is opened to vent excessive liquid from tube 100. The air pressure in tube 100 is applied to .theupper side of diaphragm 115 by means of aV conduit 120.y Air is removed from tube 100 through conduit llpasses through a filter 121 which removes any solidfmaterials..

The air then passes through a desiccant 122 and a flow regulator 123 before entering cylinder 51. This air enters cylinder 51 through an inlet port 125 and is vented through an outlet port 126 which has an explosion-proof vent therein.

The electrical circuit associated with photomultiplier tube 72 is illustrated in Figure 7. The cathode of tube 72 is connected to a potential terminal 130 which is negative with respect to a second potential terminal 131. A resistor 132 is connected between thhe cathode of tube 72 and the adjacent dynode. Similar resistors `are connected between the other adjacent dynodes. The dynode adjacent the anode is connected through a resistor 133 and a current meter 134 to ground. The anode of tube 72 is connected to the control grid of a triode 137. The anode of triode 137 is connected to a positive potential terminal 138, and the cathode of triode 137 is connected to a negative potential terminal 139 through a resistor 1413. The control grid of triode 137 is connected to ground through a resistor 141. The cathode of triode 137 is also connected through `a capacitor 142 to the first terminal of the primary winding of a transformer 143. The second terminal of the primary winding is connected to ground. The first terminal of the secondary winding of transformer 143 is connected through a capacitor 144 to first switch contacts 145 and 146. The second terminal yof the secondary winding of transformer 143 is connected to ground. A resistor 147 is connected in parallel with the secondary winding of transformer 143. The anode of a diode 148 is connected to switch 145. The cathode of diode 148 is connected to ground. A resistor 150 is connected in parallel with diode 148.

Motor 86 rotates a cam 258 between switch blades 251 and 252. This moves blades 251 and 252 into engagement with respective contacts 145 and 146 alternately. Blade 251 engages a contact 253 when blade 252 engages contact 146, and blade 252 engages a contact 254 when blade 251 engages contact 145. Contacts 253 and 254 are connected to ground through a resistor 255. The blades engage each of their contacts during approximately one-half of a cycle of rotation of cam 250. Blade 251 is connected to a servo compensating circuit to alter the gain of 72, and specifically is connected to the control grid of a triode 153. The anode of triode 153 is connected to a positive potential terminal 154, and the cathode of triode 153 is connected to a negative potential terminal 155 through a resistor 156. The cathode of triode 153 is also connected to the cathode of a diode 157. The anode of diode 157 is connected through a resistor 158 to the contactor of a potentiometer 159. One end terminal of potentiometer 159 is connected to ground, and the second end terminal is connected to a negative potential terminal 160. The anode of diode 157 is connected through a capacitor 162 to the cathode of a diode 163. The anode of diode 163 is connected to the control grid of pentode 135. The cathode of diode 163 is connected to ground through a resistor 164.

A resistor 165 and a capacitor 166 are connected in parallel with one another between the control grid of pentode 135 and ground. The anode of pentode 135 is connected through a variable resistor 168 to terminal 131. A number of series connected gas-filled discharge tube 170 are connected between the anode of pentode 135 and ground. A capacitor 171 is connected between terminal 131 and ground. The screen grid of pentode 135 is connected to a positive potential terminal 172, and the suppressor grid of pentode 135 is connected to the cathode thereof. The cathode of pentode 135 is connected to ground.

Blade 252 is connected to ground through series connected resistors 18), 181, 182` and 183'. A gain selector switch 184 is adapted to engage terminals 185, 186, 187 and 188 selectively. Switch 184 is operated by an arm 184:1, see Figure 2. Terminal 185 is connected to blade 252; terminal 186 is connected to the junction between resistors 180 and 181; terminat 187 is connected to the junction between resistors 181 and 182; and terminal 188 is connected to the junction between resistors 182 and 183. Switch 184 is connected to the control grid of a triode 194i. The anode of triode 19t)` is connected to a positivepotential terminal 191, and the cathode of triode 190 is connected to a negative potential terminal 192 through a resistor 193. The cathode of triode 190 is also connected to one end terminal of the primary winding of a transformer 194. The second end terminal of the primary winding is connected to ground. The secondary winding of transformer 194 is connected across rst opposite terminals of a full wave rectifier bridge 195. The third terminal of bridge 195 is connected through a variable resisto-r 196 and a current meter 197 to the rst input terminal of a recorder-controller 198. The fourth terminal of bridge 195 is connected to ground. A capacitor 200 is connected between ground and the junction between resistor 196 and meter 197. A variable resistor 201 is connected between ground and the junction between meter 197 and the rst input terminal of recorder-controller 198. The second input terminal of recorder-controller 198 is connected to ground.

Cam 250 is synchronized with chopper disc so that switch blade 251 engages contact when the radiation beam reected from prism 70 impinges upon tube 72. Switch blade 252 engages contact 146 when the scattered radiation beam is directed upon tube 72. The ratio of the scattered beam to the transmitted beam is a function of the solid particles in the fluid sample. When the scattered beam impinges upon tube 72., the output signal therefrom is applied through cathode follower 137, transformer 143 and switch blade 252. Diode 148 serves as a negative clamp. The signal is applied from switch blade 252 through cathode follower 190 and transformer 194 to rectifier 195. The rectied signal is filtered by resistor 196 and capacitor 280 and applied to the input of recorder-controller 198. The amplitude of this signal is a function of the solid particles in the fluid sample.

It is desired to maintain the reference beam (65-70' 72) signal relatively constant. Variations in this can be caused by changes in turbidity and by fluctuations in intensity of the light beam emitted from source 65. Compensation is accomplished when the transmitted beam is alternately directed upon tube 72. During these half cycles, the output signal from tube 72 is applied through switch blade 251 to the input of cathode follower 153. The output of cathode follower 153 is transmitted through a clipper 157 and a bias rectiiier 163 to the control grid of pentode 135. If the transmitted beam should increase in intensity, the magnitude of the negative potential applied to the control grid of pentode 135 is increased to decrease conduction therethrough. This results in the dynode potentials of tube 72 becoming less negative so that the gain of the tube is d-iminished by an amount suicient to compensate for the original change in intensity of the radiation beam. if the radiation beam should decrease in intensity, the potentials are changed in the reverse manner to increase the net gain of the photomultiplier tube. Thus, the output signal applied to recorder-controller 198 is representative solely of the solid particles of the fluid sample. Instrument 198 can be a conventional potentiometer-controller wherein an input electrical signal is converted -into a corresponding output pneumatic pressure.

A simplied form of control circuit is shown in Figure l2. This circuit is generally similar to that of Figure 7 and corresponding elements are designated by like reference numerals. The principal difference is that the switch driven by motor 86 is eliminated in Figure 12. The cathode of triode 137 is connected directly to the cathode of diode 157. The cathode of triode 137 is connected through a capacitor 142 to the control grid of triode 190. Triode 190 is provided with a single grid resistor The cathode of triode 190 is connected through, a pair of series connected electrolytic capacitors 271 and 272 tothe first terminal of the primary winding of transformer 194. The-.contactor of variable resistor 196-is connected through a. resistor 273` to one terminal of recorder 198 and through a resistor 285 to ground. One terminal of a sourcel of alternating current 28@ is connected through a capacitor 281, a rectifier 282, a resistor 283, a variable resistor 284 and resistor 28S to ground. The secondterminal of source 284)` is connected to ground. A rectifier 287 is connected between ground and the junction between capacitor 281 and rectifier 282. A capacitor 288 is connected between ground and the junction between rectifier 282 and resistor 283. A rectifierV 289 is connected. between ground and the junction between resistors 283` and 284. AC. voltage thus appears across resistors 28.4. and 285.

The output signal from tube 72 varies in magnitude at the frequency. chopper 85 is rotated. The magnitude of -this .difference is measured by recorder-controller 198 to .provide anindicationvof the-scattered flight. This signal is subtracted from the reference D C. voltage across resistors 2,84fand1285 so that recorder 198 reads up scale with an increase inturbidity of the sample being measured. The transmitted beam is of greater magnitude than thescattered beam. Thus, the greatest output signal from tube 72 is representative of the reference transmitted beam. This signal is, ineffect, compared with the bias voltage at terminal 160. Any change in the reference output signal from tube 72 thus actuates the servo compensating circuit previously described in conjunction with Figure 7. The initial relative intensities of the light beams can be adjusted by light trimmers, not shown.

In. Figure 8 there -is show-n a second embodiment of the control system of thisinvention. The product conduit 3.4 communicates through a three-way valve 211) with the inlet of either a filter 211 or a filter 212. The outlets of the two filters communicate with a three-way valve 213 w-ith the inlet of detector 3:-7.` It is assumed that valves 210 and 213y initially are opened so that the product passes through filter 211. The product stream flows in this direction until such time as the solid content may exceed a predetermined limit. At this time, the output signal from detector 37 reverses valve 38 so as to direct the product stream into disposal line 4l). Valves 210 and 2131` are also operated to divert the product stream through a fresh filter 212. When the indicated solids content decreases to an acceptable value, the operation of valve 38 is reversed to again divert the product to the storage conduit 39. If the control system operates by pneumatic pressure, as indicated, a check valve 214 can be incorporated in the control line to valves 210 and 213 to prevent the product flow fro-m reverting back to filter 211. An alarm 41 .is actuated by detector 37 to notify the operator that filter 211 needs to be replaced or reconditioned.

In Figure 9 there is shown a third embodiment of the control system. In this system the polymer product is directed at all times through a filter 216. The operation of filter 2116 normally is controlled by a differential pressure, controller 217 which adjusts a valve 218 to regulate the flow rate through filter 216. If lthe pressure differential should become too high so that excessive so-lid particles pass through the filter, these particles are indicated by the detector. The output signal from detector 37 then overrides pressure controller 217 to reduce the pressure differential. Storage and disposal conduits, such as 39 and 40 of Figure 8, can be connected to the outlet of detector 37 of Figure 9 if desired.

The control system of Figure l() combines features of the control systems of Figures 8 and 9. In the system ofy Figure 10, theflovv through either of the filters 211 and 212 normal-ly is controlled by the differential pressure cont-roller 217 which adjusts valve 218.V It is assumed that. the flow initiallygis through` filter 21.1. lf the indicated solids content should exceed a predetermined limit,

the output signal from detector 37 `diverts the flow to disposal conduit 40 and resets pressure controller 217 to reduce the rate of fiow through filter 211. A check valve 220 prevents the flow from again increasing after this initial adjustment. A flow controller 22.1V is connected in the conduit 222 which communicates between valve 213 and detector 37. Whenever the How decreases below a set value, an output air pressure from controller 221 is appliedrthrough a check valve 224 to operate valves 210 andv 213. This diverts the flow through the fresh filter 212; At the same time, the output signal from ow controller 221 operates a pulse valve 225 to vent the reset pressure initially supplied to controller 217. This permits the ow through filter 212 initially to assume a desired high value. An alarm 41 is actuated by Vcontroller 221 to notify the operator that filter 2 12 has been placed in operation.

In Figure 1l there is shown a modified form of control system which employs a centrifuge separator in place of the filter. The operation of separator 227 is controlled by the output signal of detector 37 to maintain the desired separation at all times. For example, the flow rate through the separator can be decreased if it becomes necessary to remove larger amounts of solids. A second alternative comprises adjustingthe overflow to underow rate in the separator to maintain the desired separation. These control steps are performed by the output signal from detector 37.

From the foregoing description it should be evident that various configurations of control systems can be employed in the fluid-solids `separation step of the described polymerization process. It should be evident, however, that these control systems are applicable to any fluid-solids separation. An improved nephelometer is 'alsoprovided in accordance with this invention. While the invention has been described in conjunction with present preferred embodiments, it should be evident that it is not limited thereto.

What is claimed is:

l. A nephelometer comprising a sample cell, a source of radiation, means to direct a beam of radiation from said source into said cell, a means to detect and amplify radiation, means to direct that part of the radiation transmitted through said cell from said beam to said means to detect and amplify as a first beam, means to direct that part of the radiation scattered from the first mentioned beam within said cell to said means to detect and amplify as a second beam, means to block saidfirst and second beams alternately, means to measure radiation impinging upon said means to detect and amplify from said second beam, and means responsive to said first beam impinging upon said means to detect and amplify to control the gain of said means to detectand `amplify in an inverse proportion to the ratio ofintensities between successive first beams.

2. The combination in accordance with claim 1 wherein said means to detect and amplify comprisesa photoelectric tube, and wherein said means to control comprises means to vary the operating potentials on said tube.

3. The combination -in accordance with claim 1 wherein said means to detect and amplify comprisesa photomultiplier tube, `and wherein said means to control comprises means to vary the potentials applied to the dynodes of said tube relative to the potential applied to the cathode of said tube.

4. A nephelometer comprising a sample cell; a source' of radiation; means to direct a single beam lof radiation from said source -into said cell; a photomultiplier tube; means .to direct radiation from said single Abeam that is transmitted through said cell to said tube as a first beam and means to direct radiation from said single beam that is scattered from said cell to said tube as a second beam, said first beam being of greater intensity than said second beam; means to block said first and second beams alternately; means to measure the difference between the output signals of said tube when said first and second beams impinge thereon; and means responsive to the maximum output signal of said photomultiplier tube to control the operating voltages applied to said tube so that the effective gain of said tube is varied inversely with a change -in said maximum output signal.

5. A nephelometer comprising a sample cell; a source of radiation; means to direct a single beam of radiation from said source into said cell; a radiation detector; means to direct radiation transmitted through said cell to said detector as a first beam and means to direct radi ation scattered from said cell to said detector as a second beam, said first beam being of greater intensity than said second beam; means to block said first and second beams alternately; means to measure the output of said detector; means for connecting said detector to said means to measure; means connected to said detector to vary the response of said detector inversely to changes in said first beam; and a means to provide said means to vary with a signal that is representative of the response of said detector to said first beam.

6. The nephelometer of claim wherein said means to provide includes a clipper connected between said detector and said means to vary, said clipper receiving the response of said detector to both of said first and second beams and being oppositely biased by an amount at least equal to the response of said detector to said second beam, thereby to provide said means to Vary with only a clipped response to said iirst beam.

7. A nephelometer comprising a sample cell; a source of radiation; means to direct a beam of radiation from said source into said cell; a photomultiplier tube; means to direct radiation transmitted through said cell to said tube as a first beam, means to direct radiation scattered from said cell to said tube as a second beam, said first beam being of greater intensity than said second beam; means to block said lirst and second beams alternately;

`a first circuit to vary the gain of the tube inversely with changes of the response of said tube to said tirst beam and comprising a diode clipper permanently connected to the output of said tube and biased suiiiciently to eliminate signals of said tube in response to said second beam, a dynode control vacuum tube having a control grid connected to receive the output of said clipper and said Vacuum tube being also connected to provide a current to the dynodes of said tube; a means to measure; a second circuit permanently connecting the output of said tube to said means to measure, said second circuit comprising, a full-wave rectifier connected to the output of said tube, means for biasing said rectifier at least equally and oppostely to the least in amplitude of the rectified response of said tube to said first and second beams, and means connecting the output of said biased circuit to said measuring means.

8. The nephelometer of claim 5 wherein said means for connecting includes a transformer and a rectifier connected in series to said transformer, and further includes means connected to said transformer for applying a bias to said rectifier in opposition to the respective signals re spective of the detector response to said first and second beams, said bias being equal to the least one in amplitude of such respective signals, thereby to provide said means to measure with a signal that equals the algebraic sum of said bias and the detector response to the greater in magnitude of said respective signals.

9. The nephelometer of claim 5 wherein said means for connecting said detector to said means to measure and said means connected to said detector to vary the response of said detector include switching means synchronized with said means to block so as to connect said detector to said means to measure when said second beam is received by said detector and to connect said detector to said means to vary when said first beam is received by said detector.

10. The nephelometer of claim 9 wherein said detector and said means to vary comprise a photomultiplier tube, a vacuum tube having at least an anode, a cathode and a control grid, means connecting the cathode of said vacuum tube to a point of reference potential, a direct current voltage source, means applying the negative terminal of said voltage source to the cathode of said photomultiplier tube, a resistor connected between the cathode of said photomultiplier tube and the adjacent dynode and between adjacent dynodes, means connecting the dynode adjacent the anode of said photomultiplier tube to said point of reference potential, means connected through said switching means to respond to the potential on the anode of said photomultiplier tube to apply a potential to the control grid of said vacuum tube which varies as a direct function of the potential on the anode of said photomultiplier tube; and wherein said means to measure is connected through said switching means to respond t0 the potential on the anode of said photomultiplier tube.

References Cited in the file of this patent UNITED STATES PATENTS 1,717,702 Exton June 18, 1929 2,301,367 Cahusac et al Nov. 10, 1942 2,474,098 Dimmick June 21, 1949 2,528,924 Vassy Nov. 7, 1950 2,547,212 Jamison et al Apr. 3, 1951 2,583,143 Glick Jan. 22, 1952 2,673,297 Miller Mar. 23, 1954 2,858,727 Stamm et al. Nov. 4, 1958 OTHER REFERENCES The Design of an Optical System for the Absolute Measurement of Turbidity, Journal of the Optical Society of America, Kremen et al., vol. 44, June 1954, pages 500, 501. 

